1. Technical Field
The present invention relates in general to wireless communications devices and in particular to transceiver radio frequency (RF) switches in wireless communications devices.
2. Description of the Related Art
Dual (or “simultaneous”) transmission systems provide one type of signal transmission within a first frequency band and another type of signal transmission in a second frequency band. For example, the dual transmission system may simultaneously provide voice transmissions in the BC0 band (824-849 MHz) and data transmissions in the B13 band (777-787 MHz). However, in simultaneously transmitting systems, the two transmitters that respectively provide the voice transmissions and the data transmissions may generate intermodulation (IM) signals which fall in a receive band and desensitizes a corresponding receiver. For example, third (3rd) order intermodulation signals are generated in the BC0 receive band (869-894 MHz) and the B13 receive band (746-756 MHz).
Intermodulation (IM) distortion occurs when the non-linearity of a device or system with multiple input frequencies causes the generation of undesired outputs at other frequencies. In a communications system, IM distortion occurs as signals in one channel cause interference with adjacent channels. As the communication spectrum becomes busier and channels become more tightly spaced, minimizing intermodulation distortion becomes more important.
In the dual transmission system, in order to prevent the 3rd order IM signals from desensitizing either receiver by more than 1 dB, an output IP3 (i.e., third order intercept point) level of 90 dBm is needed for front-end components. The IP3 relates nonlinear products caused by a third-order nonlinear term to the linearly amplified signal and indicates how well a receiver performs in the presence of strong nearby signals. Most front-end switches, however, cannot achieve this level of linearity associated with an output IP3 level of 90 dBm for front end components. Furthermore, conventional integrated circuit-based RF switches are not available with this level of linearity (+90 dBm IP3). In the communications industry higher linearity switches and/or filters represent a major challenge and represents an area of significant focus for development/improvement for future generations of wireless communications products.